Single frequency reuse is widely used in current state-of-the-art wireless systems, such as Long Term Evolution Advanced (LTE-A), to deal with the increasing average cell throughput with limited to no bandwidth expansion. If interference mitigation techniques are absent in these systems, the cell-edge user equipments (UEs) will suffer from strong interference from adjacent cells which degrades UE throughput. In order to improve the average cell throughput as well as the cell-edge UE throughput, a powerful interference mitigation technique is an inevitable part of wireless systems.
Different interference mitigation techniques have been proposed recently. The first interference mitigation category uses fractional frequency reuse (FFR), which is widely discussed in Long Term Evolution (LTE). In general, the concept of FFR entails allocating all available partitions of a frequency band to service UE near the center of a cell while restricting transmission to UEs near the edges of a cell to only a fraction of the available band. FFR configurations alleviate interference experienced by UEs of neighboring sectors of different cells.
Various methods for assigning frequency partitions within an FFR framework have been developed. One such method assigns each sector of a cell with a priority on a set of frequency partitions. Here, partitions to which a sector holds a higher priority are utilized for data transmission in the sector and, over time, data transmission in the sector is gradually expanded to frequency partitions to which the sector holds lower priorities. In other methods, arbitrary physical resource unit assignment is permitted and instantaneous channel gain is assumed for the utility computations. In addition, FFR schemes have been proposed in which the transmission power on each frequency partition is dynamically adjusted. However, arbitrary transmission power on each frequency partition is permitted. In these methods, complicated derivative computation is employed.
A second interference mitigation category adopts coordinated beamforming, also known as coordinated multi-point transmission (CoMP). The essence of the current CoMP schemes is to let BSs coordinate beamforming in order to reduce inter-cell interference. But the coordination requires enormous overhead on the air interface and over the backhaul since complete channel state information (CSI) needs to be shared among BSs. Moreover, although CoMP schemes may be effective in minimizing inter-cell interference, the interference may still exist along joined areas between neighboring cells
A third interference mitigation category uses rate-splitting-based interference mitigation. In rate-splitting-based interference mitigation, transmitted data streams are split into two parts: the common data stream that is decoded at a plurality of UEs, and the private data stream that is decoded only at intended UEs. By decoding the common data stream of the interference, part of the interference is canceled, and consequently UE throughput can be improved.
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